1. Field of the Invention
This invention relates to the use of entomopathogens such as viruses, bacteria, protozoa, fungi and nematodes formulated with adjuvants in compositions, as biocontrol agents.
2. Description of the Prior Art
Biocontrol agents are attractive alternatives to chemical pesticides for subduing plant pests. Their specificity for the host pest minimizes their environmental impact from a pollution standpoint. However, entomopathogens used in formulations as biocontrol agents suffer from instability after exposure to solar radiation, especially in the ultraviolet (UV) portion of the spectrum. The resulting loss of biological activity prolongs the rate at which insect pests are killed. In many instances, the pathogens lose 50% of their original activity within days.
Another important barrier to the use of biocontrol agents, especially viruses, in the management of insect pests, is that entomopathogenic viruses inherently act slowly even without the loss of activity due to UV radiation, usually requiring several days or more to achieve mortality. Larvae feed and continue to defoliate or destroy crops until shortly before death. As an example, the gypsy moth, Lymantria dispar is an insect pest of extreme environmental concern in North America, causing widespread defoliation. A nuclear polyhedrosis virus (NPV), the gypsy moth's natural entomopathogen, has been used as a biocontrol agent registered in the United States as Gypchek [Lewis, et al., U.S. For. Serv. Pap., NE-441, (1979), 9 pp.; Lewis et al., U.S. For. Serv. Pap., NE-447, (1979), 8 pp.]. Although NPV is successful in reducing gypsy moth populations, the virus is very slow acting, allowing larvae to feed almost two weeks after exposure. Therefore, field applications of virus do not provide adequate crop or foliage protection. Greater foliage protection may occur if viral activity could be increased by the addition of adjuvants [Doane and Wallis, J. Insect. Pathol., Vol. 6, (1964), pp. 423-429; Yadava, Z. Angew., Entomol., Vol. 65, (1970), pp. 175-183; Shapiro, et al., Ann., Entomol. Soc. Am., Vol. 75, (1982), pp. 346-349]. Thus, there is a need to provide biocontrol agents which provide improved environmental stability and accelerated rates of insect kill.
Several attempts have been made to increase the stability of biocontrol agents by adding UV screens such as uric acid [Teetor and Kramer, J. Invertebr. Pathol., Vol. 30, (1977), pp. 348-353; B vitamins, Shapiro, M., Environ. Entomol., Vol. 14, (1985), pp. 705-708; Congo red, Shapiro, M., J. Econ. Entomol. Vol. 82, No. 2, (1989), pp. 548-550) and activity enhancers and boric acid, Shapiro, et al., Ann. Entol. Soc. Amer., Vol. 75, No. 3, (1982), pp. 346-349] and Chitinase [Shapiro, et al., J. Econ. Entomol., Vol. 80, No. 6, (1987), pp. 1113-1116]. While these formulations provided some protection, there was still loss of activity resulting from inactivation by UV radiation. Nuclearpolyhedrosis virus (NPV) was protected using the commercially available stilbene fluorescent brightener, Tinopal DCS, at a concentration of 5% [Martignoni and Iwai, J. Econ. Entomol., Vol. 78, (1985), pp. 982-987]. While the brightener provided protection at high concentration, it did not affect pest mortality.
Stilbene fluorescent brighteners inhibit cellulose [Roberts, et al., J. Cell Biology, Vol. 9, (1981), p. 115a] and chitin [Herth, C., J. Cell Biol., Vol. 87, (1980), pp. 442-450] microfibril formation. However, these brighteners are not known as adjuvants for biocontrol. Calcofluor White prevents the assembly of cellulose microfibrils in Acetobacter xylinum by hydrogen bonding with glucan chains [Haigler, et al., Science, Vol. 210, No. 4472, (1980), pp. 903-906] and inhibits chitin synthetase activity in Neurospora crassa [Selitrennikoff, C. P., Exp. Mycol., Vol. 8, (1984), pp. 269-272].
While Calcofluor White interacts with a number of polysaccharides [Wood, P. J., Carbohydr. Res., Vol. 81, (1980), pp. 271-287] it has a high affinity for chitin and cellulose.
It can be seen from the prior art, there is an urgent need for the formulation of entomopathogens into compositions that enhance their activity.